1. Field of the Invention
The present invention relates to a spin valve magnetoresistive head, a method of manufacturing the same, and a magnetic memory apparatus and, more particularly, to a spin valve magnetoresistive head for use in a magnetic disk drive, a magnetic tape unit, etc., a method of manufacturing the same, and a magnetic memory apparatus.
2. Description of the Prior Art
In recent years, with miniaturization and increase in storage capacity of the magnetic disk drive, higher performance of the magnetic head is required. As the design of magnetic heads meet such requirements, great attention has been given to a magnetoresistive type magnetic head (referred to as a "MR head" hereinafter) which can operate without depending on the moving speed of storage medium, can be applied to a small size disk, and can output higher outputs.
AMR (anisotropic MR) head using magnetically biased conductor layers, spin valve MR head, giant MR head, and others may be considered as the MR head.
The MR head that uses the magnetically biased conductor layers, such has a structure such that part of the MR layers and lead terminals are exposed to oppose to a magnetic recording medium. In the MR head having such structure, short-circuit or discharge between the magnetic head and the magnetic recording medium is possible when a flying height of the magnetic head from the magnetic recording medium is reduced. As a result, it is feared that the magnetic head would be damaged.
The magnetic head having a structure able to overcome such a problem has been set forth in Patent Application Publication (KOKAI) 63-23217, for instance, wherein the MR layers are arranged to flow sense currents in the same direction as the signal magnetic field and only grounding lead terminals are exposed to the magnetic recording medium side. This MR head is particularly effective in a contact region between a surface of the magnetic recording medium and the MR head. The MR magnetic head having such structure is called a vertical MR head.
In addition, it is very possible that thermal asperity occurs in the MR head when the MR head collides with projections on the surface of the magnetic recording medium. The thermal asperity is expressed as a raise of the temperature of the MR device because of collision of the MR head with projections to thus increase electric resistance value.
As one countermeasure to suppress generation of the thermal asperity, a dual element type MR head has been proposed. This MR head has been set forth in, for example, Thomas C. Anthony et al., IEEE Transactions on Magnetics, Vol.30, No.2, March 1994, pp.303-308.
In these MR head, as shown in FIG. 1 for illustrative purposes only, the first MR layer 103 and the second MR layer 104 connected to leads 101, 102 respectively are arranged in parallel and sense currents passing through these first and second MR layers 103, 104 are detected in a differential manner by directing respective directions of the sense currents I.sub.1,I.sub.2 to mutually opposite directions. Simbol H.sub.sig is a signal magnetic field.
Though resistance of the first and second MR layers 103, 104 are increased respectively, as shown in FIG. 2, once the thermal asperity has occurred, in-phase components of the resistance are canceled mutually since they are detected in a differential manner. Where the sense current I.sub.1,I.sub.2 is a constant current and therefore the change in resistance appears as the change in voltage.
Furthermore, the MR head having both the above vertical MR head and the dual element type MR head has been set forth in Patent Application Publication (KOKAI) 7-21530.
However, since the MR head set forth in the Patent Application Publication (KOKAI) 7-21530 is the MR head having biased conductive layers, no mention concerning a spin valve type MR head has been given in the Patent Application Publication (KOKAI) 7-21530 since a basic structure of the former differs from that of the latter. Accordingly, it is impossible to apply the structure disclosed in this Patent Application Publication (KOKAI) 7-21530 to the spin valve type MR head as it is.